Dry silver photosensitive compositions comprise an intimate mixture of a light sensitive silver halide and another silver compound such as a silver salt of an organic acid, e.g. silver behenate or silver saccharine, which upon reduction gives a visible change and which is substantially light insensitive. Such a mixture is usually prepared in suspension and the resulting dispersion spread as a layer on a suitable substrate. When dry, the layer is exposed to a light image and thereafter a reproduction of the image can be developed by heating the layer in the presence of a reducing agent already contained in the coating.
It is because the exposure and development of the layer occur without using water, that these materials are often referred to as dry silver, light sensitive materials. Such materials are well known in the art. Minor amounts of a photosensitive silver halide, which acts as a catalyst (silver) progenitor are associated in catalytic proximity with major amounts of a heat sensitive oxidation-reduction image forming reaction mixture. The mixture reacts more rapidly in the presence of the catalyst (silver) resulting upon exposure (photoreduction) of the silver halide. Examples of such materials are described in British Patent Specification No. 1 110 046 and U.S. Pat. Spec. Nos. 3,839,049 and 3,457,075.
A wide range of reducing agents have been disclosed in dry silver systems including amidoximes such as phenylamidoxime, 2-thienylamidoxime and p-phenoxyphenylamidoxime, azines, e.g. 4-hydroxy-3,5-dimethoxybenzaldehyde azine; a combination of aliphatic carboxylic acid aryl hydrazides and ascorbic acid, such as 2,2-bis(hydroxymethyl)propionyl-beta-phenyl hydrazide in combination with ascorbic acid; a combination of polyhydroxybenzene and hydroxylamine, a reductone and/or a hydrazine, e.g. a combination of hydroquinone and bisethoxyethylhydroxylamine, piperidinohexose reductone or formyl-4-methylphenyl hydrazine, hydroxamic acids such as phenylhydroxamic acid, p-hydroxyphenyl hydroxamic acid, and beta-alanine hydroxamic acid; a combination of azines and sulphonamidophenols, e.g. phenothiazine and 2,6-dichloro-4-benzenesulphonamidophenol; alpha-cyano-phenylacetic acid derivatives such as ethyl-alpha-cyano-2-methylphenylacetate, ethyl alpha-cyanophenylacetate; bis-beta-naphthols as illustrated by 2,2'-dihydroxy-1,1'-binaphthyl, 6,6'-dibromo-2,2'-dihydroxy-1,1'-binaphthyl, and bis(2-hydroxy-1-naphthyl)methane; a combination of bis-beta-naphthol and a 1,3-dihydroxybenzene derivative, e.g. 2,4-dihydroxy-benzophenone or 2'4'-dihydroxyacetophenone; 5-pyrazolones such as 3-methyl-1-phenyl-5-pyrazolone; reductones as illustrated by dimethylamino hexose reductone, anhydro dihydro amino hexose reductone, and anhydro dihydro piperidino hexose reductone; sulphonamidophenol reducing agents such as 2,6-dichloro-4-benzenesulphonoamidophenol, and p-benzenesulphonamidophenol; 2-phenylindane-1,3-dione and the like; chromans such as 2,2-dimethyl-7-t-butyl-6-hydroxychroman; 1,4-dihydro-pyridines such as 2,6-dimethoxy-3,5-dicarbethoxy-1,4-dihydropyridine; bisphenols e.g. bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 4,4-ethylidene-bis(2-tert-butyl-6-methylphenol), and 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane; ascorbic acid derivatives, e.g. 1-ascorbylpalmitate, ascorbylstearate and unsaturated aldehydes and ketones such as benzil and diacetyl; 3-pyrazolidones and certain indane-1,3-diones.
A fundamental difference exists between the requirements of a black and white system and that of a colour system in dry silver materials. In the black and white system what is required is a black image, which is generally obtained from the silver formed. The literature discloses additives, "toners", which improve the black image. The silver itself may be formed in a variety of particle sizes and generally gives a brownish image. The toning hue cannot always be predicted. Addition of toners produces different types of silver precipitation and can be used in black and white dry silver to enhance the black colour characteristics of the image.
Examples of toners include phthalimide and N-hydroxyphthalimide; cyclic imides such as succinimide, pyrazolin-5-ones, and a quinazolinone, 3-phenyl-2-pyrazolin-5-one, 1-phenylurazole, quinazoline, and 2,4-thiazolidinedione; naphthalimides, e.g. N-hydroxy-1,8-naphthalimide; cobalt complexes, e.g. cobaltic hexammine trifluoroacetate; mercaptans as illustrated by 3-mercapto-1,2,4-triazole, 2,4-dimercaptopyrimidine, 3-mercapto-4,5-diphenyl-1,2,4-triazole, and 2,5-dimercapto-1,3,4-thiadiazole; N-(aminomethyl)aryl dicarboximides, e.g. N-(dimethylaminomethyl)-phthalimide, and N-(dimethylaminomethyl)naphthalene-2,3-dicarboximide; and a combination of blocked pyrazoles, isothiuronium derivatives and certain photobleach agents, e.g. a combination of N,N'-hexamethylene bis(1-carbamoyl-3,5-dimethylpyrazole), 1,8-(3,6-diazaoctane)bis(isothiuronium trifluoroacetate) and 2-(tri-bromomethylsulphonyl)benzothiazole); and merocyanine dyes such as 3-ethyl-5[(3-ethyl-2-benzothiazolinylidene)-1-methylethylidene]-2-thio-2,4 -oxazolidinedione; phthalazinone, phthalazinone derivatives or metal salts of these derivatives such as 4-(1-naphthyl)phthalazinone, 6-chlorophthalazinone, 5,7-dimethoxyphthalazinone, and 2,3-dihydro-1,4-phthalazinedione; a combination of phthalazinone plus sulphinic acid derivatives, e.g. 6-chlorophthalazinone plus sodium benzene sulphinate or 8-methylphthalazinone plus sodium p-toluenesulphinate; a combination of phthalazinone plus phthalic acid; a combination of phthalazine (including an adduct of phthalazine and maleic anhydride) and at least one compound consisting of a phthalic acid, a 2,3-naphthalene dicarboxylic acid or an o-phenylene acid derivative and anhydrides thereof, e.g. phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, and tetrachlorophthalic anhydride; quinazolinediones, benzo-oxazine or naphthoxazine derivatives; rhodium complexes functioning not only as tone modifiers but also as sources of halide ion for silver halide formation in situ, such as ammonium hexachlororhodate (III), rhodium bromide, rhodium nitrate and potassium hexachlororhodate (III); inorganic peroxides and persulphates, e.g. ammonium peroxydisulphate and hydrogen peroxide; benzoxazine-2,4-diones such as 1,3-benzoxazine-2,4-dione; 8-methyl-1,3-benzoxazine-2,4-dione, and 6-nitro-1,3-benzoxazine-2,4-dione; pyrimidines and asym-triazines, e.g. 2,4-dihydroxypyrimidine, 2-hydroxy-4-aminopyrimidine, and azauracil, and tetrazapentalene derivatives, e.g. 3,6-dimercapto-1,4-diphenyl-1H,4H-2,3a,5,6a-tetrazapentalene, and 1,4-di(o-chlorophenyl)3,6-dimercapto-1H,4H-2,3a,5,6a-tetrazapentalene.
A substantially different result is desired in a colour system. One does not want a black or grey silver image as this affects the overall colour intensity and rendition of the dye species. A number of methods have been proposed for obtaining colour images with dry silver systems. Such methods include incorporated coupler materials, e.g. a combination of silver benzotriazole, well known magenta, yellow and cyan dye-forming couplers, aminophenol developing agents, a base release agent such as guanidinium trichloroacetate and silver bromide in poly(vinyl butyral); a combination of silver bromoiodide, sulphonamidophenol reducing agent, silver behenate, poly(vinyl butyral), an amine such as n-octadecylamine and 2-equivalent or 4-equivalent cyan, magenta or yellow dye-forming couplers; incorporating leuco dye bases which oxidises to form a dye image, e.g., Malachite Green, Crystal Violet and para-rosaniline; a combination of in situ silver halide, silver behenate, 3-methyl-1-phenylpyrazolone and N,N'-dimethyl-p-phenylenediamine hydrochloride; incorporating phenoic leuco dye reducing agents such as 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-4,5-diphenylimidazole, and bis(3,5-di-tert-butyl-4-hydroxyphenyl)phenylmethane; incorporating azomethine dyes or azo dye reducing agents; silver dye bleach process, e.g. an element comprising silver behenate, behenic acid, poly(vinyl butyral), poly(vinyl-butyral) peptized silver bromiodide emulsion, 2,6-dichloro-4-benzenesulphonamidophenol, 1,8-(3,6-diazaoctane)bis-isothiuronium-p-toluene sulphonate and an azo dye was exposed and heat processed to obtain a negative silver image with a uniform distribution of dye which was laminated to an acid activator sheet comprising polyacrylic acid, thiourea and p-toluene sulphonic acid and heated to obtain well defined positive dye images; and incorporating amines such as aminoacetanilide (yellow dye-forming), 3,3-dimethoxybenzidine (blue dye-forming) or sulphanilanilide (magenta dye-forming) which react with the oxidised form of incorporated reducing agents such as 2,6-dichloro-4-benzene-sulphonamido-phenol to form dye images. Neutral dye images can be obtained by the addition of amines such as behenylamine and p-anisidine.
There has been a very strong, specific continuing need for improved photothermographic materials for providing a developed image in colour. Ideal characteristics required for the image forming dyes are as follows:
(a) the dye precursors should assist in the toning action of the silver to give as low a visual density of silver metal as possible, PA1 (b) the dyes must have a hue suitable for three colour reproduction, PA1 (c) the dyes must have large molecular extinction coefficients, PA1 (d) the dyes must be stable to light, heat and in the presence of other additives in the system, such as the dye releasing activator, PA1 (e) the dye precursors must be easily synthesised. PA1 R.sup.1 represents H, CN, lower alkyl of 1 to 5 carbon atoms, aryl or COOR.sup.6 in which R.sup.6 is lower alkyl of 1 to 5 carbon atoms or aryl of up to 8 carbon atoms, PA1 R.sup.2 and R.sup.3 independently represent CN, NO.sub.2, COOR.sup.6, SO.sub.2 R.sup.6, CONHR.sup.6 in which R.sup.6 is as defined above, or R.sup.2 and R.sup.3 together represent the necessary atoms to form a 5- or 6-membered carbocyclic or heterocyclic ring having ring atoms selected from C, N, O and S atoms, which carbocyclic or heterocyclic rings possess at least one conjugated electron withdrawing substituent, PA1 R.sup.4 and R.sup.5 independently represent H, CN or lower alkyl of 1 to 5 carbon atoms or together represent the necessary atoms to complete a 5- or 6-membered carbocyclic ring, and PA1 Ar represents:
It has been found that a range of benzylidene leuco compounds are capable of dye formation in dry silver systems.